Page:Popular Science Monthly Volume 24.djvu/482

466 passes, and heated by plunging into warm water; when the temperature is reached at which the test is to be made, the cylinder is briskly shaken, the stopper removed, and a small flame introduced. Flashing-points obtained by this plan are considerably lower than those given by the methods which have been discussed, and are found, moreover, to be largely independent of the conditions so essential to success in the latter.

Haass has described an elaborate and clever apparatus based on the same principle, and differing essentially from Meyer's only in the substitution of an electric spark, at a fixed distance from the surface of the oil, for the flame which the latter employed. In both of these methods the flashing-point depends upon the time allowed between the shaking and testing, Haass recommending an interval of one minute after the bubbles have disappeared from the surface of the oil, in order to permit the suspended oil-particles to settle. The shaking, which must be repeated from degree to degree, is a troublesome feature of these methods, and, though Meyer's apparatus is certainly simple and inexpensive enough, that of Haass is difficult of construction, electrical, and costly. The general principle of these methods is, however, without question the correct one for obtaining a minimum (and approximately "absolute") flashing-point, and it is to L. Liebermann that we owe the suggestion of an ingenious and successful plan for



avoiding the difficulties mentioned above. In Liebermann's method the saturation of air with vapor is accomplished by forcing an air-current through the oil as it is warmed from degree to degree; and the test made by bringing a small flame to the mouth of the oil-holder at the same instant.

It has, however, been shown that the intermittent current of air which is recommended gives somewhat irregular results, and that more concordant flashing-points are obtained by letting a continuous current